Improve unsupported target message (#630) #105

Job	Run time
host-x86 (x86_64, g++-10)	2m 8s
host-arm (armv7, none, none, g++-10)	3m 45s
host-x86 (x86_64, clang++-11)	52s
host-win (x86_64)	42s
host-arm (armv7, none, none, clang++-11)	3m 36s
coding-style	10s
host-win (armv7)	42s
host-arm (aarch64, none, none, g++-10)	2m 53s
host-win (aarch64)	38s
host-arm (aarch64, none, none, clang++-11)	3m 59s
host-win-msvc	1m 39s
host-arm (aarch64, crypto+crc, none, g++-10)	3m 13s
host-arm (aarch64, crypto+crc, none, clang++-11)	3m 48s
host-arm (armv7, none, -mcpu=cortex-a32 -mfpu=neon-fp-armv8, g++-10)	3m 57s
host-arm (armv7, none, -mcpu=cortex-a32 -mfpu=neon-fp-armv8, clang++-11)	3m 43s
test-win-msvc	55s
	36m 40s

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